Flexible control of positive and negative electrocaloric effects under multiple fields for a giant improvement of cooling capacity

摘要

This paper demonstrated the flexible control of positive and negative electrocaloric effects (ECEs) in 〈001〉-Pb(Mg_(1/3)Nb_(2/3))_(0.7)Ti_(0.3)O_3 single crystal, and a dual cooling cycle is proposed using their combination to improve cooling capacity. The ECE exhibits a complex evolution of positive-negative-positive within 20-140 °C, where the negative ECE originates from the electric field-induced transition from rhombohedral phase to high-symmetric tetragonal phase. Since the coexistence of different ECEs at some temperatures, the positive and negative ECEs alternately appear in neighboring cycles under proper applied fields, i.e., dual cooling. A significant improvement of ∼150% in cooling capacity is directly characterized by the isothermal heat flow measurement.